The present invention relates to an electrically driven hand-held apparatus for body care such as a toothbrush or a massage apparatus.
Known electrical toothbrushes of this kind have a direct current motor in the apparatus casing constructed in the form of a handgrip; the motor may be connected to the main supply network or may be fed from a battery, and its rotary motion is converted by means of a motion transformer to an oscillatory movement of the pushed-on toothbrush about its longitudinal axis. For this purpose a support in form of a disc provided with an eccentric pin is mounted on the motor shaft, and the inner end of the instrument holder has a radially extending fork attached thereto, the eccentric pin engaging between the arms thereof; the longitudinal axis of the instrument holder is radially offset relatively to the axis of rotation about which the eccentric pin circulates, that is to say relatively to the motor axis or the axis of rotation of the disc, respectively, in such a manner that the rotating eccentric pin affords the instrument holder with the toothbrush pushed thereon an oscillatory motion of constant oscillation amplitude about the shank of the toothbrush.
Such an oscillatory movement of the toothbrush is particularly effective for the care of teeth and mouth and permits above all an optimum message of the gums which is important for maintaining the health of the teeth and the gums; oscillation frequencies of the toothbrush of between approximately 40 and 60 Hz have been found most favourable for this purpose.
However, experience has shown that the sensitivity of the gums and the teeth to the brushing or the message, respectively, differs widely from person to person, and in particular in the case of a gum disease, above all paradontosis, injuries and bleeding may occur even by careful brushing with a normal brush. The pain threshold, also, is very different individually. In order to take account of these individual physiological conditions, the user of an electrical toothbrush heretofore had in general only the possibility to use attachable toothbrushes with sufficiently soft bristles, and he had to take care that he did not press the brush down too hard. A reduction of the supply voltage of the motor would have the unfavourable consequence of a reduction of the rotary speed of the motor and thus a reduction of the oscillation frequency of the brush, thereby disadvantageously affecting the message effect; moreover the gums would be stressed as before in as much as it is squeezed to and fro through a path corresponding to the unchanged oscillation amplitude; when the gums are sensitive or diseased, this may lead to tearing the tissue even at a relatively low message frequency.
A reduction of the mechanical energy or output of the oscillating treatment instrument without reduction of the oscillation frequency is frequently desirable even for general body massage apparatus, in order to be able to perform appropriately careful massages of sensitive or inflamed body regions or for example for the purpose of make-up.
An electrical toothbrush of the kind described above is already known, in which a change of the distance between the longitudinal axis of the instrument holder and the axis of rotation of the support for the eccentric pin is provided, so that thereby the oscillation amplitude can be adjusted within certain limits. This is attained by the fact that either the motor with the disc supporting the eccentric pin is mounted in the casing in a radially displaceable manner, or that the eccentric pin is located on a gearwheel which is mounted adjacent the motor shaft on a bearing plate and which meshes with a pinion secured on the motor shaft, and the entire bearing plate can be rotated about the motor shaft. However, the first mentioned construction with a radially displaceable motor necessitates a complicated constructional design of the apparatus, in which case additionally the diameter of the apparatus casing must be correspondingly increased in an unfavourable manner; likewise the rotatable mounting of the entire bearing plate with the gearwheel carrying the eccentric pin in accordance with the other known constructional form and the necessary arrangement of the operating element for the adjustment of the bearing plate are very unfavourable in a constructional respect, and furthermore, upon displacement of the bearing plate in the peripheral direction of the casing, obviously also the rest position of the toothbrush, or the entire angular range of the toothbrush oscillation is twisted relatively to the apparatus casing, respectively; this renders convenient manipulation of the apparatus difficult.